Tooth sensitivity affects numerous people. It is often caused by eating or drinking something hot, cold, sweet or acidic. Under normal conditions, the papal chamber, which houses the blood vessels and nerves, is surrounded by the dentin, which in turn is covered by the enamel in the tooth crown, and the gums that surround the tooth. Over time, the enamel covering can get thinner, thus providing less protection. The gums can also recede over time, exposing the underlying root surface dentin.
The dentin contains a large numbers of pores or tubule orifices that run from the outside of the tooth to the nerve at its center. When the dentin is exposed, these tubule orifices can be stimulated by temperature changes or certain foods. The hydrodynamic theory of dentin sensitivity states that stimuli applied to exposed dentin tubule orifices cause a movement of fluids in the tubules which, in turn, stimulates nerves in the pulp.
The well-know Pashley method for determining dentin permeability has been used as an in vitro model for screening agents which have been used to desensitize dentin. In this method, fluid is forced from an inlet across (or through) one side of a dentin disc sample to the other side and, then, its flow rate measured to determine the rate of fluid flow across the dentin sample. The prepared disc sample of dentin is secured in a split-chamber device, clamped between two paired “O” rings.
Certain limitations, however, exist regarding the Pashley method and generally relate to inherent inaccuracies affecting the overall accuracy of the method's permeability measurements. Moreover, the design of the flow cell used in the Pashley method does not allow for easy removal of the dentin sample during dentin permeability analysis to, for example perform further challenge to the dentin sample's surface and, then, return the dentin sample back to the flow cell for continued analysis.
Another limitation of the Pashley method relates to its inability to standardize the flow rates obtained across different dentin samples when permeability data for more than one dentin sample is necessary or desired.
As a result of these limitations, large sample sizes are required to achieve statistically significant dentin permeability readings.
The search for faster and more accurate methods of measuring the permeability of dentin using a modified flow cells and/or permeability measurement methods continues. Desired aspects for these methods include high accuracy and throughput (i.e., performing technology testing quickly and reliably producing sound data), data separation, error reduction, robustness, repeatability, and use with additional testing methods.